Prospective cohort studies of bowel movement frequency and laxative use and colorectal cancer incidence in US women and men

Purpose The associations between bowel movement frequency, laxative use, and colorectal cancer incidence remain uncertain. No published studies have accounted for potential latency between these factors and colorectal cancer onset. Methods We prospectively examined these associations among 88,173 women in the Nurses' Health Study (NHS, 1982-2010) and 23,722 men in the Health Professionals Follow-up Study (HPFS, 2000-2010). Cox proportional hazards regression models were used to estimate multivariable hazard ratios (HRs, 95 % CIs). We conducted time lagged analyses to evaluate the potential latency in the NHS. Results We documented 2,012 incident colorectal cancer cases. The HRs (95 % CIs) for infrequent bowel movement relative to daily were 0.86 (95 % CI 0.71-1.04) in women and 0.81 (95 % CI 0.48-1.37) in men. The HRs for weekly to daily relative to never laxative use were 0.98 (95 % CI 0.81-1.20) in women and 1.41 (95 % CI 0.96-2.06) in men. In women, the HRs for every 3 days or less bowel movement relative to daily were 0.87 (95 % CI 0.59-1.27) for colorectal cancers that developed within 10 years of assessment, 1.03 (95 % CI 0.85-1.26) for 11-18 years after assessment, and 0.73 (95 % CI 0.54-1.01) for 19-28 years after assessment. The corresponding HRs for weekly to daily relative to never laxative use were 0.93 (95 % CI 0.63-1.37), 1.03 (95 % CI 0.74-1.44), and 0.98 (95 % CI 0.71-1.35), respectively. Conclusion Bowel movement frequency and laxative use appear not to be associated with colorectal cancer risk in this study.